1. Field of the Invention
This invention relates generally to chairs for use in offices for example. More particularly, the invention relates to chairs of the type wherein the chair seat and/or the chair back are designed to be tiltable at least rearward against a spring or springs.
2. Description of the Prior Art
There have been proposed various types of tiltable chairs wherein at least one of the chair seat and the chair back is tiltable against a tilting control spring or springs. The most typical is a rocking chair wherein the seat is rearwardly tiltable together with the chair back. Such a chair enables the user to assume a relaxing posture occasionally during desk work for example.
As is well known, the degree of tilting of a tiltable chair seat and/or back is generally proportional to the weight of the user but inversely proportional to the spring constant of a tilting control spring or springs. Thus, for a given weight, the tilting degree increases with decreasing spring constant, and decreases with increasing spring constant.
Most commonly used as a tilting control spring is a coil spring whose spring constant is invariable. Thus, a tiltable chair utilizing a tilting control coil spring or springs has a disadvantage that the tilting degree inevitably varies depending on the weight of a particular user with no possibility of adjusting the spring constant.
U.S. Pat. No. 4,077,596 discloses a chair tilting control assembly which comprise a pair of tilting control plate springs each fixed at one end in a cantilever fashion for elastically allowing rearward tilting of the chair seat. Specifically, the weight of the sitter applied to the seat is elastically supported by the plate spring via a U-shaped rod which provides a load applying member carried by the seat. The U-shaped rod is designed to be advanced or retreated relative to the plate spring by manually turning an adjusting screw. Thus, the spring constant of the plate spring can be adjusted to suit the weight of the user.
However, the tilting control assembly of the above U.S. patent is disadvantageous in that it requires manual adjustment upon every change of the user. Further, the manual adjustment is cumbersome and time-taking, so that the user often prefers uncomfortable chair tilting than making such adjustment. Moreover, the manual adjustment is a guess game, and therefore does not necessarily result in comfortable chair tilting.